feat(control-center): P1 pipeline core — stage machine, decisions, artifacts, leases, SSE
- pipeline: 8-stage order, NextStage (testing skippable), gate pure
functions (agents may never advance; only in_progress->awaiting_review)
- tasks: domain layer over cc_* tables — CRUD, claim/heartbeat/release
leases, advance-request, decisions with strict suggestion validation,
stage transitions, external submit, stage settings, overview, lease reaping
- server: agent + console routes, SSE broker broadcasting every event
insert, 60s lease reaper goroutine, 1MB body limit, domain error mapping
- archtest: allowlist controlcenter/* and engineeringdashboard packages
weichen
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